1. Field of the Invention
This invention relates to a mechanism for transmitting and switching the driving power of a motor used for a camera.
2. Description of the Related Art
Cameras of the kind performing film winding and shutter charging by means of a built-in motor are known. Generally, an electromagnetic motor is employed as a drive source for cameras of this kind. However, a vibration motor such as an ultrasonic motor, (hereinafter abbreviated to USM), has recently come to be employed as a drive source for a camera.
These motors have their own characteristics. The electromagnetic motor gives a high output despite its compact size. The electromagnetic motor, however, makes a loud operating sound because of its high speed rotation. In the case of the USM, the motor makes no operating sound and gives a high torque with its low speed rotation. Thus, an advantage of the USM lies in that the rotating speed of gears of a driving power transmission system connected to the motor is also low, so that the operating sound of the whole driving system of the camera including the motor can be greatly reduced. The USM, however, requires a higher driving voltage than the electromagnetic motor and thus necessitates increased battery voltage. Hence, in terms of efficiency as a drive source, the USM is inferior to the electromagnetic motor. It is, therefore, not easy to obtain a high output from the use of the USM.
In view of the difference in characteristics. between these motors, it has been common practice to use the electromagnetic motor for a high-performance camera equipped with a high speed shutter having shutter speed as 1/8000 sec. and arranged to perform such speed film winding high as up to five frames of film per second, and to use the USM for a camera which silently operates.
However, in accordance with the conventional arrangement, a high-performance camera inevitably makes a loud operating sound. Also, it has previously not been possible to arrange a silent camera capable of winding up to five frames per second with a high speed shutter having a maximum shutter speed of 1/8000 sec.